In one form of respiratory therapy, the patient receives oxygen or a mixture of oxygen and air. In order to avoid dehydration, discomfort, and damage to the lungs, it is necessary that the gas be humidified to a high moisture content. Certain treatment calls for a dense aerosol or mist of water droplets to be carried by the oxygen or mixture to the patient (generally by means of a tent). This is accomplished in present practice, either by use of a venturi nebulizer operated by the oxygen stream, or when an extremely dense fog is indicated, by means of an ultrasonic nebulizer. In many cases, however, the use of a mist is contraindicated, and the present invention is concerned with a device that will provide, as prescribed, either a high level of humidification of oxygen delivered with a minimum of entrained droplets, or a dense aerosol in oxygen or air/oxygen mixture.
In a common form of humidifier in the prior art, one simply passes bubbles of the gas, generated in some form of sparger, up through a head of water contained in a reservoir. This method is unsatisfactory in that the humidity obtainable is low and is not constant, diminishing as the level of water in the container falls as it vaporizes during the course of treatment. Also, bubbles are objectionably noisy.
Another method available is described in U.S. Pat. No. 3,913,843 (Cambio). This device employs the same venturi nebulizer conventionally used to create an aerosol or mist, then entrains the droplets in a foraminous member, so that only the humidified gas passes into the exit stream to the patient. The aerosol droplets are entrained and the liquid is returned to the reservoir by an extra tube which is somewhat of a nuisance and may also be the source of pressure leaks. The foraminous member is described as a reticulated polyurethane foam or any foraminous material, such as a microporous filter in which the atomized droplets may be entrained or interstitially held. This device is less than satisfactory in that the filter causes an appreciable pressure drop, the maximum humidity obtainable at high flow-rate is insufficient, and the maximum flow rate may be too low.
In the application of respiratory therapy, it is highly desirable that sterile water be used to humidify the oxygen stream, and it is advantageous that the container be a factory-filled and sealed, disposable package. Designs which may cause contamination of the sterile water (or medicament) when assembled at bedside are not satisfactory.
Prior U.S. patents which show humidifiers include U.S. Pat. Nos. 3,836,079; 2,709,577; and 3,652,015. U.S. Pat. No. 3,075,523 shows a nebulizer which includes a series of mesh screens designed to demist the larger aerosol droplets.